PROTON THERAPY

What is proton therapy?

Proton therapy is a form of radiation therapy that destroys cancer cells by preventing them from dividing and growing - the same as with standard X-ray radiation. Proton therapy uses protons - heavy, positively charged atomic particles - instead of the photons used in standard X-ray radiation therapy.

Protons can be precisely conformed to release most of their energy directly in the tumor, greatly reducing damage to nearby healthy tissue. As a result, patients often can receive higher, more effective doses and generally have far fewer side effects from treatment.

How does proton therapy work?

Protons can be manipulated to release their energy at precise depths so they can target tumors near the skin surface or deep inside the body, depositing most of their radiation exactly at the tumor site. The peak of this proton radiation dose (called the Bragg Peak) is set so it releases the radiation when it hits the tumor; immediately after that point, the radiation dose falls to almost zero. Less radiation reaches the healthy tissue in front of the tumor, and almost none reaches the healthy tissue behind the tumor, resulting in much less damage to healthy tissue. Patients often experience fewer short-term and long-term side effects that typically accompany standard X-ray radiation. In addition, because more radiation can be deposited directly in the tumor, a higher dose often can be delivered, leading to more effective treatment.

How do proton beams destroy cancer cells?

When protons reach the nucleus (or center) of cancer cells, they transfer energy to the cells' electrons causing a series of interactions, or ionizing events, that damage the DNA of the cancer cells. The damaged cells are permanently injured, can no longer divide, and die.

Is proton therapy experimental?

No, proton therapy is not experimental. Proton therapy was approved by the U.S. Food and Drug Administration (FDA) to treat patients in 1988. It has been used to treat patients since its first medical application in mid-1950s and Medicare and Medicaid began covering the procedure in 2000.¹ To date, more than 60,000 people worldwide have received proton therapy at centers in Europe, Asia and the United States.

What is the history of proton therapy?

In 1946, physicist Robert Wilson first proposed that protons could be used to deliver an increased dose of radiation to a tumor while simultaneously decreasing the exposure of surrounding healthy tissue to radiation.

By 1950, the first research trials were being conducted on patients in Europe. Results were promising, but the inability of imaging technology to accurately "see" or locate many tumors, as well as the inability to direct protons to sites deep within the body, meant that only a few patients were appropriate candidates for the treatment.

Advances in imaging, including computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET), now allow physicians to "see" deep inside the body and precisely define the location, size and shape of tumors. This capability, coupled with improvements in proton technology, brought about today's growing interest in proton therapy as an important treatment option for cancer.

The first hospital-based proton treatment center in the United States was built in 1990 at Loma Linda University Medical Center (LLUMC) in Loma Linda, California. As of February 2010, seven facilities were operating in the United States: ProCure Proton Therapy Center, Oklahoma; Francis H. Burr Proton Therapy Center at Massachusetts General Hospital; the Midwest Proton Radiotherapy Institute at Indiana University; the Proton Therapy Center at the M.D. Anderson Cancer Treatment Center; The Roberts Proton Therapy Center at the University of Pennsylvania; the Florida Proton Therapy Institute at the University of Florida Shands Medical Center; and LLUMC. In addition, there is a specialty proton center that treats only cancers of the eye at the University of California, Davis.

When was proton therapy first used for medical purposes?

Proton therapy was first used to treat patients in Berkeley, California, in 1955 in a research setting. While promising, it wasn't until advances in imaging technology, such as CT, MRI and PET scans, allowed doctors to accurately "see" the location, size and shape of cancer tumors. Accurately locating tumors made it possible to leverage the precision of protons. The first U.S. center opened at Loma Linda University Medical Center in 1990. More than 20 centers have opened in the past 20 years, and by 2008, there were 29 centers worldwide.

How many patients have received proton therapy?

Since the first hospital-based proton treatment center opened in California in 1990, nearly 30,000 people have received proton therapy in the United States, and more than 60,000 people worldwide.² Experts conservatively estimate that about 250,000 cancer patients in the U.S. could benefit from proton therapy.

What kinds of studies have been/are being done to prove the effectiveness of proton therapy?

The effectiveness of proton therapy has been studied by researchers around the world. There is a growing number of studies that report on the effectiveness of proton therapy and its benefits compared to alternative treatments. The amount of research being conducted on proton therapy is rapidly increasing as more centers open and more patient experiences become available.

A bibliography of select articles and presentations is available.

Can proton therapy be used in combination with other cancer treatments?

In many cases, yes. Proton therapy can be used in combination with chemotherapy, as a follow-up treatment to surgery and in combination with standard X-ray radiation treatment.

What are the potential side effects of proton therapy?

Patients should not feel pain or discomfort during treatment sessions. There may be side effects during or after treatment, but they are generally minor, less frequent and less severe than the side effects that can result from standard X-ray radiation therapy, primarily because less healthy tissue is exposed to radiation in proton therapy. Potential side effects may include skin reactions in the direct path of the proton radiation, fatigue and temporary hair loss. Depending on the tumor site treated, different side effects may be experienced. Your doctor will discuss with you the specific side effects that you may experience based on your treatment plan.

TYPES OF CANCER THAT MAY BENEFIT FROM PROTON THERAPY

What are some of the common tumor sites treated with proton therapy?

Certain types of cancer are more appropriate for proton therapy than others. While research continues to support using protons in more types of tumors, they are primarily used to treat:

• Brain tumors
• Head and neck tumors
• Base-of-skull tumors
• Prostate cancer
• Pediatric tumors
• Tumors near the spine
• Melanoma (cancer) of the eye
• Paranasal sinus tumors
• Lung tumors
• Arteriovenous malformations

Proton therapy is particularly appropriate for treating tumors in children, who typically experience more serious short-term and long-term side effects from radiation treatments than adults.

Learn more about tumor sites that can benefit from proton therapy.

Can proton therapy be used for all types of cancers in all patients?

Proton therapy is not appropriate for all types of cancers or all patients. Proton therapy is most effective on solid tumors (including but not limited to those found in the head, brain, neck, lung and prostate) that are well-defined and localized - those that have not spread to other areas of the body. If the tumor has spread (metastasized), proton therapy may not be an appropriate treatment. Only a healthcare provider can determine the best approach for a patient's unique condition.

Why is proton therapy only an option for a certain types of cancer?

Because of the limited number of proton treatment facilities worldwide, physicians have focused on using proton therapy primarily for tumors near critical organs, such as the heart and bladder, or structures, such as the spine. The types of tumors treated will continue to expand as research continues and doctors develop treatment plans for more types of tumors.

Can proton therapy be used to treat children with cancer?

Yes, in fact proton therapy is particularly effective for children who need radiation therapy. Clinical studies indicate that proton therapy reduces the risk of growth and developmental problems, as well as secondary tumors which can occur years later. Because their bodies are small and still growing, the damage to nearby healthy tissue and organs from standard X-ray radiation can be harmful. This damage can cause growth abnormalities, reductions in IQ and other complications. New tumors can also develop later in the child's life. A growing body of research is confirming the advantages of the use of proton therapy for children.

Can proton therapy be used to treat recurrent cancers?            

In many cases, yes. Proton therapy can be used to treat recurrent cancers that standard X-ray radiation therapy cannot. Patients should discuss proton therapy with a board certified radiation oncologist to determine if it can be beneficial.

COMPARISON OF PROTONS AND PHOTONS

How is proton therapy different from standard radiation treatment?

Proton beams deposit most of their energy directly in the tumor, reducing damage to healthy tissue and allowing patients to receive higher, more effective doses. Less damage to healthy tissue and organs can result in fewer side effects than sometimes experienced with standard X-ray radiation therapy, thus improving patients' quality of life and long term health. X-ray radiation can be harder to control and deposits more radiation in healthy tissue as it enters and leaves the body.

Are X-rays (photons) as effective as protons in destroying tumors?

X-rays and protons can be equally effective in destroying cancer tumors. The difference is that X-ray treatments damage more healthy tissue in the process. X-rays release much of their energy quickly after penetrating the skin, damaging healthy tissue and organs on their way to the tumor and, again, as they leave the body. Protons can be precisely directed to release most of their energy when they reach the tumor. Because there is much less damage to healthy tissue, a higher dose often can be delivered with protons, leading to more effective treatment.

Why is proton therapy often considered a better treatment option compared to standard X-ray radiation therapy?

Because proton beams deposit more of their energy directly in the tumor, less radiation reaches the healthy tissue in front of the tumor, and almost none reaches the healthy tissue behind the tumor. Patients often experience fewer short- and long-term side effects that typically accompany standard X-ray radiation therapy. In addition, because more radiation can be deposited directly in the tumor, a higher dose often can be delivered, leading to more effective treatment.